The present invention relates to vascular catheters and devices, and more specifically to a control device for deploying self-expanding medical devices. Vascular catheters and devices are currently employed in a variety of medical procedures. These procedures often require manipulation (or actuation) of the vascular device by a mechanism located outside the patient""s body. The present invention is specifically useful in deploying self-expanding medical devices, such as a self-expanding stent or graft, within a patient""s vasculature.
Catheters have long been used in intraluminal procedures for various medical needs. They generally are made from elongated tubes which may be placed within various body lumens. A common use for catheters is the treatment of vascular diseases. Such procedures usually involve the percutaneous introduction of an interventional device into the lumen of the artery, usually through the catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The uninflated balloon catheter is initially inserted into the patient""s arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the vessel, resulting in increased blood flow. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature. Enhanced blood flow should now resume in the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In the procedure of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the injured area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent can be crimped onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
A variety of stent designs have been developed and include self-expanding stents insertable and deliverable through the patient""s vasculature in a compressed state for deployment in a body. Unlike balloon expandable stents which rely on an external radial force to expand the stent at the area of treatment, self-expanding stents are made from materials which are self-expanding in order to move between a compressed or collapsed position to an expanded, implanted position. Stent delivery catheters used for implanting self-expanding stents usually include an inner member upon which the compressed or collapsed stent is mounted and an outer restraining sheath placed over the stent to maintain it in its compressed state prior to deployment. When the stent is to be deployed in the body vessel, the outer restraining sheath is retracted in relation to the inner member to uncover the compressed stent, allowing the stent to immediately move into its expanded condition for implantation in the patient.
Vascular grafts also can be implanted within a body vessel utilizing a delivery catheter which is percutaneously introduced into the patient""s vasculature system. These types of grafts may include a number of self-expanding rings, or small stents, placed along a flexible tubular member that forms a conduit once implanted in a body vessel. Vascular grafts are utilized to bypass diseased and weakened body vessels, such as when an artery experiences an aneurysm which weakens and abnormally expands the artery. In this manner, the vascular graft will act as a conduit for blood to flow freely there through, bypassing the diseased portion of the arterial wall caused by the aneurysm. As a result, the chances that the artery could possibly rupture due to pressure build-up in the artery is greatly reduced. Self-expanding vascular grafts also can be mounted onto a delivery catheter which includes a restraining sheath placed over the entire vascular graft, including the self-expanding rings, in order to maintain the graft in a collapsed position. Once the physician is able to manipulate the vascular graft into the desired location in the patient""s vasculature, the simple retraction of the restraining sheath from the vascular graft will cause the self-expanding rings or stents to expand and contact the wall of the body lumen in which the graft is implanted.
These various treatments at the intraluminal site typically require the manipulation of the catheter system, a portion of which remains external to the patient""s body. The physician must actuate the catheter system to retract the restraining sheath in order to properly deploy the stent or vascular graft in the body vessel. Actuator mechanisms which can be located at the proximal end of the catherter system may be as simple as a control handle attached to the restraining sheath that can be manipulated by the physician to retract the restraining sheath from the self-expanding medical device. During the placement of a stent or graft, it is important that the retraction of the restraining sheath be performed while the main catheter, on which the stent or graft is mounted, remains stationery in the body lumen. Some control mechanisms for retracting the restraining sheath requires that some force be applied by the physician in the longitudinal direction of the delivery catheter (i.e., in an axial direction). This force, in turn, can be transmitted to the main catheter assembly which can cause the stent or graft to move from the desired location within the body lumen. As the physician retracts the sheath, if the main catheter holding the stent or graft moves proximally with the sheath out of the target area, precision placement of the medical device will not be accomplished. Therefore, when a physician uses this type of device, the mere act of retracting the restraining sheath can sometimes result in inaccurate placement of the medical device within the body vessel.
Another problem exists when self-expanding stents or grafts which have an appreciable length (for example, 60 mm and longer) are to be deployed. These larger devices usually are more difficult to deploy accurately using existing catheter systems because a long retraction stroke is needed to retract the distal end of the restraining sheath from the medical device. In such cases, the physician may experience some difficulties in moving the proximal control device the required length to fully expose the self-expanding medical device. Moreover, the deployment of longer stents and grafts may require higher forces to retract the restraining sheath due to frictional forces which can be generated between the stent or graft and the restraining sheath as the sheath is being retracted. Therefore, the physician may have to apply more force to adequately retract the restraining sheath when a long stent or graft is being implanted. Thus, when a long stent or graft is being implanted, a physician may find it difficult to manipulate the proximalcontrol device while maintaining the remainder of the catheter system stationary to prevent the stent or graft from moving from the desired area of implantation.
Thus, what has been needed is a control mechanism which helps to provide a more precise deployment of a self-expanding medical device within the body vessel to reduce the chances that the physician may inadvertently move the medical device from the intended area of treatment. An improved control device is also needed when a long stent or graft to be deployed to reduce the actuating force which is needed to retract the sheath the required distance. Such a device also should reduce the length of the actuating motion which must be applied to the control device when retracting the restraining sheath. The present invention satisfies these and other needs.
The present invention provides a control device and mechanism for retracting a restraining sheath used in conjunction with self-expanding medical devices, such as self-expanding stents and vascular grafts, for implantation in a patient""s vasculature.
The control device and mechanism of the present invention are particularly advantageous since the actuating mechanism allows the physician to retract the restraining sheath from the self-expanding medical device by using a motion that is at an angle to the line of motion of the restraining sheath, which should help to prevent movement of the catheter portion of the control device within the patient In one particular aspect of the present invention, the actuating motion can be substantially perpendicular to the line of motion of the proximal end of the restraining sheath. As a result, the physician""s manipulation of the control device, when retracting the restraining sheath, should not place a displacing force on the inner portion of the catheter which could otherwise cause the stent or graft to move from the target area. A more accurate placement of a stent or graft can thus be accomplished by the physician since the possibility of stent or graft movement is reduced when the restraining sheath is being retracted. The control mechanism also allows the physician to deploy a longer stent or graft with a shorter actuating motion to reduce the amount of manual actuation performed by the physician when retracting the restraining sheath. As a result, the physician only needs to push a thumb knob or trigger a short distance to cause the restraining sheath to retract a larger distance to fully expose the medical device for implantation. The present invention also can use springs or biasing members to reduce the amount of force needed to push the knob or trigger. As a result, a physician will find that it is much easier to manipulate a control device made in the present invention especially when longer stents or vascular grafts are being deployed in the patient""s vasculature.
In one aspect of the present invention, the control device utilizes a movable rack and pinion mechanism for retracting the proximal end of the restraining sheath while maintaining the inner catheter portion, on which the self-expanding medical device is mounted, stationary. The physician can grasp the control device and utilize his/her thumb to push a control knob attached to the moveable rack which causes rotation of a pinion and an attached pulley. Rotation of the pulley causes a timing belt to translate along the housing of the control device to move a slider member towards the pulley. The slider is attached to the proximal end of the restraining sheath so that when the slider is retracted proximally by the control mechanism, the distal end of the restraining sheath also will be retracted proximally the same distance to expose the stent or vascular graft. The moveable rack is designed to translate in a direction set at an angle, usually between 30xc2x0 to 90xc2x0, to the line of motion defined by the slider/restraining sheath. As a result, when utilizing this type of mechanism, the physician does not have to move the control device in the same axial direction as the motion of the restraining sheath to retract the sheath for deployment purposes. Thus, the chances of the stent or vascular graft becoming displaced from the desired area of implantation in the body vessel is greatly reduced.
In another aspect of the present invention, the ratio of the pulley pitch diameter to the pinion pitch diameter can be increased to allow the physician to retract the restraining sheath a longer distance with only a minimal amount of actuating distance when manipulating the control knob. As a result, a long stent or graft can be more easily deployed with a minimal amount of actuating movement required by the physician. The moveable rack also can be spring loaded in order to reduce the amount of force needed to move the control knob when retracting the restraining sheath. In this manner, the physician does not need to use as much strength when using the actuating mechanism, which is especially useful when a long stent or vascular graft is being deployed. In this manner, the spring or biasing element utilized in conjunction with the moveable rack assists in pushing the movable rack along with the actuating motion provided by the physician.
It is to be understood that the present invention is not limited by the embodiments described herein. Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.